LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Sun Sep 03 2023
Valid 031300Z - 041200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN NEVADA AND WESTERN UTAH...
...SUMMARY...
Isolated severe gusts and hail are possible across much of the
Intermountain West this afternoon and evening. Severe gusts may
concentrate over parts of eastern Nevada and western Utah.
...Synopsis...
The mid/upper-level pattern will become much more progressive over
the western CONUS, as an initially cut-off low near Cape Mendocino
devolves to a strong, open-wave trough and shifts inland. By 00Z,
the trough should extend from eastern OR southward across the
central/northern Sierra to coastal southern CA. By 12Z, it should
reach southwestern MT, southeastern ID, and the eastern border of
NV. The mid/upper trough should be preceded by a related low-level
cold front moving eastward across the Great Basin toward the
central/northern Rockies. The 00Z front should be located across
central MT, western WY, northwestern UT, and central NV. By the end
of the period, this front should extend from a low over western ND
southwestward through the central Rockies to southern UT, with a lee
trough southward over the central High Plains.
As the mid/upper trough advances eastward, the longstanding high/
ridge over the south-central Plains will weaken. However, the
cut-off low now over north TX will remain too far from associated
height falls for any substantial influence until day 2, and in the
meantime, will meander erratically near its present position.
General thunderstorm potential will continue in an area of favorable
low-level moisture and difluent mid/upper winds from near the low to
its east and southeast, across the lower Mississippi Valley and
portions of the Gulf Coast States.
...Intermountain West...
Widely scattered to scattered thunderstorms are possible along/ahead
of the cold front this afternoon into evening, as an expansion/
extension of ongoing, initially nonsevere activity over northwestern
NV and southeastern OR. Isolated severe gusts and perhaps hail
could be observed almost anywhere over a vast area of the
Intermountain region and Great Basin. Within that, a relative
concentration of severe-gust potential in particular appears
possible across parts of northwestern UT and eastern NV.
A longstanding plume of moisture advection/transport from
subtropical latitudes, contributing for extensive convective
activity and precip the past few days over swaths of this area, will
persist and even expand today, under increasing influence from the
accelerating mid/upper trough. Large-scale lift -- both from warm
advection and DCVA -- will destabilize the mid/upper levels
somewhat, with already weak MLCINH essentially vanishing in areas
that can experience sustained diurnal heating. A midlevel dry slot
evident in satellite imagery may foster such destabilization over
parts of eastern NV/western UT, with resultant convection moving
northeastward over somewhat well-mixed boundary layers of lower
ground elevations. Modified model soundings suggest peak MLCAPE in
the 800-1300 J/kg range over the 15% wind area, amidst 35-45 kt
effective-shear magnitudes. As such, a blend of supercells and
multicells is possible, with some clustering of the latter further
contributing to local wind potential. Isolated large hail also will
be possible, mainly with any sustained supercells.
..Edwards/Leitman.. 09/03/2023
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